/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.flink.runtime.state;

import java.io.ObjectStreamException;

/**
 * Singleton placeholder class for state without a namespace.
 */
public final class VoidNamespace {

	// ------------------------------------------------------------------------
	//  Singleton instance
	// ------------------------------------------------------------------------

	/** The singleton instance */
	public static final VoidNamespace INSTANCE = new VoidNamespace();

	/** Getter for the singleton instance */
	public static VoidNamespace get() {
		return INSTANCE;
	}

	/** This class should not be instantiated */
	private VoidNamespace() {}

	// ------------------------------------------------------------------------
	//  Standard Utilities
	// ------------------------------------------------------------------------

	@Override
	public int hashCode() {
		return 99;
	}

	@Override
	public boolean equals(Object obj) {
		return obj == this;
	}

	@Override
	public String toString() {
		return getClass().getSimpleName();
	}

	// ------------------------------------------------------------------------
	//  Singleton serialization
	// ------------------------------------------------------------------------

	// make sure that we preserve the singleton properly on serialization
	private Object readResolve() throws ObjectStreamException {
		return INSTANCE;
	}
}